Proteins and proteolysis in pre-term and term human milk and possible implications for infant formulae

Understanding the differences between the protein system of human milk and bovine milk is critical in the development of infant formulae. In this study, the proteins of bovine milk and a bovine-based whey-dominant infant formula were compared with those of human milk for infants born prematurely (pre-term) or at full term (term). The protein distribution of infant formula differed significantly from that of either type of human milk. A proteomic comparison between pre-term and term human milk showed a reduction of levels of β-casein and α_s-casein and appearance of additional products, corresponding to low molecular weight hydrolysis products of the caseins, in pre-term milk. Pre-term milk samples also had higher total nitrogen concentration and plasmin activity, consistent with the proteomic data. These results suggest the operation of a physiological mechanism that may adjust enzyme and/or protein expression to modify protein digestibility, and may facilitate design of infant formulae, closer to maternal milk, particularly for premature infants.